Vehicle air conditioners conventionally include a compressor driven by an internal combustion engine of the vehicle so as to provide cooling of the vehicle passenger compartment during warm weather. The power demand on the engine during acceleration with the air conditioner operating is relatively high and results in significant fuel usage that lowers the engine efficiency. Likewise, an increased power demand on the engine such as when the vehicle climbs a hill with the air conditioner operating also results in high fuel usage and lower engine efficiency. Of course, the ever-increasing scarcity and cost of fuel makes it more and more desirable to increase the efficiency of vehicle engines.